Blue stain may be avoided by which of the following methods?

The correct answer is based on the understanding that blue stain in wood typically results from certain fungi that thrive in damp conditions and can be exacerbated by the presence of iron from steel wool. When steel wool is used in woodworking, the iron particles can oxidize and create conditions favorable for the growth of these fungi, leading to the formation of blue stain.

Thus, avoiding steel wool is a preventive measure against blue stain. This method focuses on eliminating a potential contributing factor that promotes the conditions under which blue stain fungi thrive. In contrast, the other methods like careful sanding, bleaching, or avoiding water-based stains do not specifically address the source of the issue related to steel wool and iron contamination.

Careful sanding may help to remove some surface imperfections but does not prevent the underlying conditions that cause blue stain. Bleaching can help lighten the appearance of blue stain once it has occurred, but it does not prevent it from developing in the first place. Avoiding water-based stains may be prudent for other reasons, but it does not directly relate to the prevention of blue stain, which is primarily linked to fungal activity rather than the type of stain used.